A linear particle accelerator (linac) accelerates charged particles using a series of oscillating electric potentials generated by RF cells joined together to form a linear beamline. At one end of the linac, the particles from a particle source are injected into the beamline using a high voltage. The typical design process for a linear accelerator requires careful consideration of the coupling parameters between adjacent cells. These structures are fed from one single point or input guide and the power flows from that point to all cells through coupling holes which typically also serve as the beam tunnel for the particles being accelerated. Coupling between cells limits the ability of designers to optimize the cell shape for efficiency (high shunt impedance) and power and gradient handling capability.
Commonly owned U.S. Pat. Appl. Pub. 20140191654 entitled “Distributed Coupling High Efficiency Linear Accelerator”, which is incorporated herein by reference, describes a practical implementation of a microwave circuit that is capable of separately feeding multiple cavities while minimizing the coupling between cavities. This design, however, has a somewhat complicated structure in the case of coupling to each cavity. In the case of coupling to every few cavities, it has a simple structure but at the expense of a reduced efficiency. Accordingly, there remains a need for further improvement in efficient linac design.